In the bulk or solution polymerization of one or more monomers, it is generally necessary to remove unreacted monomer, dimers, trimers, oligomers, and diluent, if present, from the resulting polymers. In one method the polymer melt, from the reactor is pumped by a gear pump to a heater on top of a vertical vacuum chamber. The heater is typically a tube and shell type heat exchanger, and the tubes open into the top of the vacuum chamber. The polymer melt flows through the tubes of the heat exchanger and should form strands of melted polymer descending to the bottom of the vacuum chamber. The residual monomer, dimers, trimers, oligomers, and diluent if present devolatilize out of the falling polymer strands, causing them to foam.
The preheater and devolatilizer are operated hot to reduce the viscosity of the melt. This should permit the bubbles of volatile material in the melt to rise to the surface of the melt more rapidly. While this is true, the less viscous melt descends to the bottom of the devolatilizer faster and there is less time for the volatiles in the melt to diffuse to the surface of a strand of polymer melt. There has been a need to increase the dwell time of the polymer melt in a form which provides a high surface to volume ratio.
One early attempt to achieve this was to provide projections, or cones (the so called chinese hats). In theory the falling strands of polymer melt impacted on the surface of the cone; ran down the side of the cone, then continued to the bottom of the devolatilizer as an annulus of melted polymer. In practice, the polymer melt does not always have a uniform viscosity so that "blobs" of polymer may fall out of the annulus of melted polymer. The result is that the devolatilization is less efficient than expected, and there is a high standard deviation in the devolatilization of the polymer.
U.S. Pat. No. 3,694,535 issued Sept. 26, 1972 discloses an annular distributor to be used in a falling strand devolatilizer. The distributor of U.S. Pat. No. 3,694,535 is of an open top type, rather than close top as required by the present case. Furthermore, the distributor does not suggest a tray as required in the present case.
U.S. Pat. No. 4,744,957 issued May 17, 1988 may be of interest. It discloses a devolatilizer with a head which extrudes polymer film. The patent fails to teach the projection and tray required in the present case.
Applicants co-pending U.S. patent application Ser. No. 507,740 filed on even date herewith discloses a horizontal polymer melt distributor. The distributor comprises in combination a "candy scoop" shaped distributor and a tray beneath the distributor. The co-pending patent application fails to teach the projection of the present invention. Furthermore the "candy scoop" distributor uses a significantly different preheater exit than in a conventional falling strand devolatilizer.
The present invention overcomes the drawbacks of the prior art and provides a novel distributor which helps reduce the content of monomer, dimer, trimer, oligomer and diluent, if present, in a polymer melt from a reactor. Additionally, the present invention provides a polymer melt distributor which results in a lower standard deviation in the residual levels of monomer, dimer, trimer, and diluent in devolatilized polymer.